It is often desirable to store immunologically active antigens in a dry form to increase shelf-life. In order to accomplish this, the aqueous antigens must be dehydrated in a manner that preserves their antigenicity. Conventional methods for preserving antigenic materials from sensitive biological samples include freeze drying, spray drying, spray freeze drying and foam drying. Dehydrating an antigen usually results in a highly soluble powder, which can be rehydrated at the time of use.
Carrier molecules are conventionally added to the aqueous preparations prior to dehydration to protect the sensitive biological samples from thermal and mechanical degradation during the drying process. These carriers have been necessary to preserve the biological activity and antigenicity of the dehydrate product (Maa et al., 2007, Current Drug Delivery, 4:57-67; Chen et al., 2010, Vaccine, 28:5093-5099; Amorij et al., 2008, Pharmaceutical Research, 25(6):1256-1273).
Lipopolysaccharide (LPS) is found in the outer membranes of gram-negative bacteria. LPS can induce inflammation and endotoxic shock in many species. In order to produce vaccines against gram-negative bacteria it is often necessary to remove the LPS to reduce unwanted tissue site reactions, fever, inflammation and the risk of shock. Some of the conventional methods to reduce LPS include purification of proteins by ion-exchange chromatography, affinity adsorbents, gel filtration chromatography and ultrafiltration (Magalhães et al., 2007, J. Pharmacy Pharmaceutical Sci., 10(3):388-404). The choice of purification method is dependent on the biochemical properties of the antigen and the LPS.
In addition to purification and preservation concerns, the proteins used as vaccines are often weakly antigenic and require adjuvants to stimulate a protective immune response in the host. Examples of common adjuvants include aluminum hydroxide, mineral oil emulsions, Freund's adjuvant, virus-like particles, QS-21 and MF59 (Vaccine Adjuvants, Edited by O'Hagan, D., 2000, Humana Press).